[video="youtube;--1LBnOcHhQ"]https://www.youtube.com/watch?v=--1LBnOcHhQ[/video]
But seriously, I can relate. Honestly, what has helped me most is anger. Convincing myself, even though objectively it was quite a nuanced situation, that she was s**tty to me and that it's good riddance. This doesn't seem very possible in your situation given that everything was amicable, but I'd certainly recommend cutting ties with him. If that seems too harsh, I guess you ought to find someone new, I suppose; that's pretty sure to help you forget.